The present invention relates generally to print heads having electromagnetic print wire actuators for use in a dot matrix printer and particularly to the print heads, the mounting for the print heads and a method of assembling the print heads on a printer carriage.
Conventional print heads for dot matrix printers typically employ a substantial number of actuators, for example, 6, 11 or 22, mounted behind a long wire guide. The wire guide is normally a flat plate with print wire holes accurately machined to provide precise centerline-to-centerline spacing for the print wires. Alternatively, the print wires may be accurately spaced using a special service gauge. Each actuator normally includes an electromagnetic coil which, when actuated, drives a piston along a bore driving a print wire in front of the piston against the bias of a spring. Of course, the advance of the print wire causes it to engage an ink transfer medium (e.g., an inked ribbon) and apply a dot to a print medium (e.g., paper). By properly timing the individual print wire drive pulses to each actuator in conjunction with paper and print head movements, a printed dot of ink can be placed at virtually any desired location on the paper, thus to form alphanumeric or other symbols, as is well known in the art. Typically, one or more print heads are mounted on a shuttle which rapidly oscillates in a horizontal direction while the paper is indexed in a transverse direction each time the print head nears one of its horizontal travel limits. Typically, the print actuator array is oscillated at an amplitude which is slightly more than the regular spacing between print wires in the print head so as to permit placement of a dot at every possible dot position along a given print line before the paper is indexed to a new dot print line.
One common goal in the design of actuators is to make them as small as possible because of the need to array a plurality of the actuators in a relatively small volume to facilitate close spacing of individual print wires within a dot matrix print head. It is quite common, therefore, to provide print heads having a substantial number of actuators. When multiple print heads each comprising a large number of actuators, i.e., six or more, are mounted to or behind a long wire guide with accurately pre-positioned print wire holes, it is frequently necessary to replace the entire print head, including all of the six of more actuators, as a result of the failure of but one actuator. Accuracy in the initial placement and the replacement of the print head is also required and difficult to attain. Further, the spacing between print wires of various printers is also different one from the other, requiring accurate machining of precisely spaced holes along the long wire guide for receiving the print wires. Even where service gauges are used to space the actuators, this is a laborious and oftentimes inaccurately performed task. Consequently, these constraints render actuator and mounting designs therefor quite difficult, particularly in identifying, removing and replacing a failed actuator, in a manner to achieve precise accurate alignment of the print wires.
According to the present invention, there is provided a print head, a mounting for the print head and a method of mounting the print heads which minimizes or eliminates the foregoing and other problems associated with prior print heads, mountings therefor and methods of mounting and provides novel and improved print heads, mountings therefor and methods of assembly. Particularly, a print head according to the present invention includes a print head support for mounting a pair of actuators in side-by-side relation on one side thereof and having a pair of openings for receiving the print wires. Wire guide supports are provided on the opposite side of the print head support in line with and for receiving the print wires. The wire guide supports are preferably screw-threaded on externally threaded sleeves which extend through the print head support openings from corresponding actuators whereby threading the wire guide support onto the sleeve clamps each actuator and associated wire guide support to and on opposite sides of the print head support. A wire guide is provided adjacent the distal end of the wire guide support for receiving the wire and guiding it toward the ink transfer medium.
In accordance with the present invention, the pair of wire guide supports for each print head define a plane passing through edges thereof. More particularly, the wire guide supports are preferably cylindrical in external configuration and, when disposed side-by-side in a print head, define a horizontal plane tangent to their cylindrical configurations. The print head support also has a flat or linear extending surface which forms a predetermined angle, preferably a right angle, with the tangent plane. Consequently, the print head has surfaces accurately defining a predetermined, preferably right, angle with one another for facilitating mounting of the print heads to the shuttle carriage in a dot matrix printer.
In order to mount the print head of the present invention in the printer, there is provided a bar or carriage, carried by the shuttle of the dot matrix printer, having two flat, angularly related surfaces which correspond in angular relation to the angle between the flat surface of the print head support and the tangent plane defined by the wire guide supports. These surfaces are preferably right angularly related to one another, similarly as the print head support surface and tangent plane are preferably right angularly related. Thus, the print head is applied to the bar or carriage with the wire guide supports bearing on one of the flat surfaces of the bar or carriage, i.e., in a horizontal plane, and the linear surface of the print head support bearing along the other angularly related, i.e., vertically extending, surface of the bar or carriage. The print head support may then be secured to the bar or carriage, for example, by a single screw or bolt coupling the print head support and the carriage one to the other.
It will be appreciated that the shuttle mounted carriage includes a plurality of print heads mounted in side-by-side relation to one another. By fabricating the wire guide supports to a lateral dimension, i.e., an outside diameter, corresponding identically to the centerline-to centerline spacing of the print wires, the print heads can be readily disposed side-by-side and achieve the exact and desired centerline-to centerline spacing of the print wires. Thus, in mounting the print heads, the sides of the wire guide supports abut one another and, in that relation, accurate centerline to-centerline spacing of the print wires is obtained. This mounting therefore defines a straight line of equally spaced print wires, i.e., the print wires are precisely spaced one from the other along a horizontal line.
With this construction, there is also afforded the flexibility to change the centerline-to-centerline dimension of the print wires by providing print head supports of a different size and varying the diameter of the wire guide supports. More particularly, the openings through the print head supports are spaced one from the other corresponding to the desired centerline-to-centerline spacing of the actuator wires. The wire guide supports are formed to diameters corresponding to the centerline-to-centerline spacing of the print wires. Bore holes are provided in the shuttle carriage at different elevations therealong corresponding to a number of different centerline-to-centerline spacings between print wires. The print head supports have elongated slots for securing the print heads to the carriage. Thus, by mounting the print heads along the carriage with the wire guide supports in contact with one another and securing the print heads to the carriage by bolts passing through the slots in the print head support, the mounting of print heads with different centerline-to-centerline spacing can be readily achieved.
Additionally, with the foregoing invention, there is low investment by the printer user in actuator replacement. In the present invention, only a pair of actuators is mounted to each print head support. Consequently, when an actuator fails and after the failed actuator is identified, only the print head mounting the pair of actuators containing the failed actuator need be removed and replaced. Thus, there is the expense of replacing only one additional serviceable actuator when replacing the failed actuator. This is in contrast to removing an entire array of actuators, testing them and attempting to replace the failed actuator or replacing the entire array of actuators.
In a preferred embodiment according to the present invention, there is provided a method of assembling a print head on a support frame having a pair of elongated angularly related support surfaces, the print head having a print head support with a linear surface, an actuator carried by the print head support and having an actuator wire and a wire guide support for the actuator wire mounted on the print head support and projecting therefrom to form a predetermined angle with the linear surface of the print head support, comprising the steps of mounting the print head on the support frame by engaging the wire guide support on one of the angularly related surfaces, engaging the linear surface of the print head support on the other of the angularly related surfaces of the support frame and thereafter securing the support frame and print head support one to the other.
In a further preferred embodiment according to the present invention, there is provided a print head for mounting on a support member comprising a pair of print head actuators, each actuator carrying a print wire, a print head support for mounting the pair of actuators and having openings for receiving respective print wires. Means are provided for securing the pair of actuators and the print head support one to the other on one side of the print head support with the print wires extending through the openings, with a wire guide support for each actuator and having a passage therethrough for receiving the print wire and means for retaining the wire guide support on the print head support on the opposite side thereof from the actuator, the wire guide supports lying in side-by-side relation one to the other defining a first plane passing along edge portions thereof, the print head support having a linear surface along the opposite side thereof defining a second plane angularly related to the first plane for mounting the print head on a support member having corresponding angularly related surfaces.
In a further preferred embodiment according to the present invention, there is provided a print head assembly for a dot matrix printer comprising a plurality of print heads, each print head including a pair of print head actuators each carrying a print wire, a print head support for mounting the pair of actuators and having openings for receiving respective print wires, means for securing the pair of actuators and the print head support one to the other on one side of the print head support with the print wires extending through the openings, a wire guide support for each actuator and having a passage therethrough for receiving the print wire and means for retaining the wire guide support on the print head support on the opposite side thereof from the actuator, a support member having a pair of angularly related surfaces, said print heads being disposed in side-by-side relation to one another on the support member, wire guide supports on each adjacent pair of print heads lying in side-by-side relation one to the other defining a first plane passing along edge portions thereof, each print head support having a linear surface along the opposite side thereof defining a second plane angularly related to the first plane identically as the surfaces of the support member are angularly related to one another whereby the print heads are mounted on the support member with the edge portions of the wire guide supports and the linear surfaces engaging the corresponding angularly related surfaces of the support member.
Accordingly, it is a primary object of the present invention to provide a novel and improved print head, mounting therefor and method of mounting a print head in a dot matrix printer wherein accurate alignment of the print wires in true centerline-to-centerline spacing and ready installation and replacement of print heads are achieved.
These and further objects and advantages of the present invention will become more apparent upon reference to the following specification, appended claims and drawings.